Crystal Axes Research Articles

Simulation and Measurement of Stray Fields for the Manipulation of Spin Qubits in One- and Two-Dimensional Arrays.

The inhomogeneous magnetic stray field of micromagnets has been extensively used to manipulate electron spin qubits. By means of micromagnetic simulations and scanning superconducting quantum interference device microscopy, we show that the polycrystallinity of the magnet and nonuniform magnetization significantly impact the stray field and corresponding qubit properties. The random orientation of the crystal axis in polycrystalline Co magnets alters the qubit frequencies by up to 0.5 GHz, compromising single qubit addressability and single gate fidelities. We map the stray field of Fe micromagnets with an applied magnetic field of up to 500 mT, finding field gradients above 1 mT/nm. The measured gradients and the lower magnetocrystalline anisotropy of Fe demonstrate the advantage of using Fe instead of Co as magnets in spin qubit devices. These properties of Fe also enabled us to design a 2D arrangement of nanomagnets for driving spin qubits distributed on a 2D lattice.

Study on the diffusion model of two dimensional T type planar network

In this paper, we proposed a memory diffusion model of molecules on T-type planar network. This model regards the diffusion of molecules in zeolite as a jump from one adsorption site to another adjacent adsorption site. The probability of the jump is a composite probability, which includes both the probability provided by the transition state theory and the information from which direction the target molecule comes. This method gives an expression for the influence of the memory effect on the anisotropy of molecular diffusion under different conditions, revealing that the diffusion coefficients along the two crystal axes on the zeolite are related. Taking AWO zeolite as an example, the diffusion anisotropy of five simple molecules, CF4, Xe, CH4, N2, and Ar, in AWO zeolite was studied by molecular dynamics method. The main factors affecting the diffusion in zeolite were proposed, and the importance of memory effect in the molecular diffusion inside zeolite was verified.

Second Harmonic Generation with 48% Conversion Efficiency from Cavity Polygon Modes in a Monocrystalline Lithium Niobate Microdisk Resonator

AbstractThin‐film lithium niobate (TFLN) based optical microresonators offer large nonlinear coefficient d33 and high light‐field confinement, allowing highly efficient second‐order optical nonlinear frequency conversion. Here, ultra‐efficiency SHG from high‐Q polygon modes is achieved by maximizing the utilization of the highest nonlinear coefficient d33 in a monocrystalline X‐cut TFLN microdisk resonator for the first time. The polygon modes are designed and formed with two parallel sides perpendicular to the optical axis of the lithium niobate crystal by introducing weak perturbations into the microdisk through a tapered fiber, which maximizes the utilization of d33. The polygon modes exhibit ultrahigh intrinsic Q factors up to 3.86 × 107, due to the fact that polygon modes are located far from the relatively rough sidewall of the microdisk. Moreover, the pump and second harmonic polygon modes share high modal overlap factor of ≈80%. Consequently, SHG from cavity polygon modes with absolute conversion efficiency as high as 48.08% is realized at an on‐chip pump level of only 4.60 mW without fine domain structures, surpassing the best results (23% and 30%) reported in other two domain‐inversion‐free phase matching schemes and even approaching the record (52%) in periodically poled TFLN microresonators.

Research on the Modulation Characteristics of LiNbO3 Crystals Based on the Three-Dimensional Ray Tracing Method

To further study the electro-optical modulation characteristics of LiNbO3 crystals and analyze their modulation performance, a method for studying the modulation characteristics of LiNbO3 crystals, based on the three-dimensional ray tracing method, is introduced. With the help of the refractive index ellipsoidal theory, the optical properties of LiNbO3 crystals under the influence of the Pockels effect are systematically investigated. The research results show that the optical properties of LiNbO3 crystals under the action of an external electric field can be divided into two cases: the crystal optical axis is parallel to the clear light direction, and the crystal optical axis is perpendicular to the clear light direction. Subsequently, starting from Maxwell’s equation and the matter equation, the analytical expressions of optical parameters such as refractive index, wave vector, light vector, optical path, and phase delay in electro-optical crystals are derived. Finally, the propagation law of LiNbO3 crystals when the light is incident in any direction, i.e., when the optical axis of the crystal is parallel to the clear direction and perpendicular to the clear direction, and the light intensity and field of view of the LiNbO3 crystal for electro-optical modulation are discussed.

Magnon and electromagnon excitations in Dy0.9Nd0.1FeO3 single crystals tuned with temperature and magnetic field

Magnon and electromagnon excitations in RFeO3 (where R is a rare-earth element) are associated with the orderings of Fe and R ions, respectively, both of which strongly depend on temperature and applied magnetic field. Herein, by employing the magnetic and electric components of terahertz radiation, we have investigated the temperature and magnetic field dependent magnon and electromagnon excitations in Dy0.9Nd0.1FeO3 single crystals. Our results demonstrate that a small fraction of Nd-substituted Dy ion in Dy1−xNdxFeO3 (with x = 0.1) single crystals shows negligible influence on quasi-ferromagnetic (q-FM) and quasi-antiferromagnetic (q-AFM) modes when the temperature is above TNR, the ordering temperature of rare-earth ions. By contrast, introduction of 10% doping concentration of Nd element leads to changes in exchange interaction of rare-earth ions, consequently altering the frequencies of the electromagnon. Applying magnetic field along different crystal axes can tune the frequency of both q-FM and q-AFM modes and even trigger Fe3+-based spin reorientation phase transition. Furthermore, application of magnetic field can suppress the ordering of rare-earth ions and electromagnon excitation. We anticipate that our findings can advance the understanding of magnetoelectric coupling mechanisms and pave the way for the development of advanced multiferroic materials with tailored properties.

Field-free spin–orbit torque switching of Mn-doped L10-FePt layer

Spin–orbit torque (SOT) switching of the L10-FePt single layer has attracted a lot of interest in recent times. Herein, we report the tunability of switching performance in L10-FePt films by Mn doping. The results show that field-free switching can be realized by Mn doping, and the switching performance exhibits an angular dependence with respect to the crystal axis. Such switching behavior can be attributed to cone anisotropy induced by Mn doping. In addition, the SOT efficiency can be enhanced by Mn doping. These results can deepen our understanding of the SOT-induced switching of L10-FePt films.

Chiral Phonon, Valley Polarization, and Inter/Intravalley Scattering in a van der Waals ReSe2 Semiconductor.

Exploring valley manipulatable layered semiconductors is highly significant for valleytronic devices. Here, we report the phonon chirality and resulting inter/intravalley scattering in valley polarized van der Waals (vdW) layered ReSe2 by linearly/circularly polarized Raman (L/CPR), transmission (L/CPT), and photoluminescence (L/CPL) spectroscopic techniques. L/CPR combined with scanning transmission electron microscopy determines the Re chains' direction and displays the existence of chiral phonons. The LPT discloses the energetic valley polarization between the Re chains and its perpendicular crystal axis directions. Intriguingly, the valley polarization strength depends on the layer thickness even in a micrometer scale and abnormaly increases with temperature increase. Further, CPT manifests the optical rotation in ReSe2 due to strong chiral phonon-photon coupling. More essentially, L/CPL unveils a strong exciton-like effect (Stokes shift) that can be interpreted from the inter/intravalley scattering related to the (chiral) phonon-carrier coupling. This investigation suggests a promising platform based on a low-symmetry vdW ReSe2 semiconductor for exploring valley physics and fabricating valley(opto)tronic nanodevices.

φ Josephson Junction Induced by Altermagnetism.

We study the Josephson effect in a superconductor-altermagnet-superconductor junction. We find anomalous phenomena, including 0-π transition and multinodal current-phase relations. Similar to a d-wave superconductor, a d-wave altermagnet can support a φ junction where free-energy minima locate neither φ=0 nor ±π with double degeneracy. These properties can be tunable by parameters, e.g., the exchange energy, the orientation of crystal axis, the length, and the chemical doping of the altermagnet. These rich features lead to accessible functionality of superconductor-altermagnet-superconductor junctions.

Precise Bottom-up Synthesis of Functional Nanowires and Nanosheets Based on 1D and Quasi-1D Van Der Waals Crystals

Anisotropy often leads to unexpected structures and properties in the solid state. In van der Waals (vdW) solids composed of 1D or quasi-1D (q-1D) building blocks, anisotropy in both intra- and inter-chain directions results in an abundance of crystalline packing motifs and drastically altered physical states. Among these, 1D/q-1D vdW solids that display topologically protected states, confined photonic modes, and direct band gap characteristics in few- to single-chains are highly sought after due to their tremendous potential as building blocks for next-generation quantum computing, spintronic, and telecommunication devices. Yet, access to such facet- and edge-specific physical states is still limited by the stochastic nature of micromechanical exfoliation. Here, we present two convergent efforts that address the growth of 1D and q-1D vdW crystals, which have closely related stoichiometric competing phases or exhibit rich polymorphism. First, I will describe the unique crystallization behavior of Bi4I4, a known topological insulator in bulk, in the presence of Au nanoparticle (NP) catalysts. Systematically varying Au NP diameters, Bi:I precursor ratios, and growth-deposition temperatures reveals that Au NPs generally act as nucleation sites for the vapor-solid (VS) growth of Bi4I4 nanowires. Strikingly, we discovered that post-synthesis analysis of 20 nm Au NPs, showing an equistochiometric 1:1 ratio of Bi to I within the Au NP, distinctly triggers the vapor-liquid-solid (VLS) growth of [001]-oriented quasi-2D nanosheets comprised of laterally-ordered [Bi4I4]n chains along the perpendicular [100] direction. Second, I will discuss how highly anisotropic and intrinsically strong covalent interactions along the long axis in 1D vdW crystals enable the uncatalyzed growth of record-long photonic nanowires (approximately 8 mm long with thicknesses ranging from 30 to 60 nm) via bottom-up vapor-phase routes. In both systems, we employ a series of structural and spectroscopic techniques to establish the structure, polytype, and physical properties of the well-defined nanowires and quasi-2D nanosheets that emerge from our synthetic routes.

Second-order nonlocal shifts of scattered wave-packets: What can be measured by Goos–Hänchen and Imbert–Fedorov effects?

The scattering of wavepackets with arbitrary energy dispersion on surfaces has been analyzed. Expanding up to second order in scattering shifts, it is found that besides the known Goos–Hänchen or Imbert–Fedorov spatial offset, as well as the Wigner delay time, new momentum and frequency shifts appear. Furthermore, the width of the scattered wave packet becomes modified as well, which can lead to a shrinking of pulses by multiple scattering. For a model of dielectric material characterized by a longitudinal and transverse dielectric function the shifts are calculated analytically. From the Goos–Hänchen and Imbert–Fedorov shifts one can access the longitudinal and transversal dielectric function. Perfectly aligned crystal symmetry axes with respect to scattering beam shows no Imbert–Fedorov effect. It is found that the Goos–Hänchen and Imbert–Fedorov effect are absent for homogeneous materials. Oppositely it is found that the Wigner delay time and the shrinking of the temporal pulse width allows to access the dielectric function independent on the beam geometry.

Formation Behavior of Nanoholes in Porous Ga Oxide

Fabrication processes of porous Ga oxide have attracted attention due to its useful semiconductor properties of Ga oxide that allow completely decomposing water. The porous Ga oxide is expected to be applied to various energy conversion devices, such as hydrogen generation devices. The performance of the devices highly depends on their geometrical structures in addition to their semiconductor properties. Therefore, to improve the device performance, geometrical control of the porous Ga oxide is important. One of the fabrication processes of the porous Ga oxide is an anodization process. An advantageous point of the anodization process is the good controllability of the geometrical structures of the nanohole array. Until now, our group has reported the fabrication process of porous Ga oxide having an ideally ordered nanohole array structure by the anodization process utilizing a pretextureing process [1]. This pretexturing process had been originally proposed to fabricate an ideally ordered anodic porous alumina [2]. Prior to the anodization, an ideally ordered array of nanometer-sized concaves was formed onto the surface of Ga metal by the pretexturing process. During the anodization of the textured sample, the nanoholes preferentially grew from each concave, then, an ideally ordered nanohole array was obtained. However, the formation of straight nanoholes having a high aspect ratio was difficult although various anodizing conditions were considered. In the present research, the formation of a porous Ga oxide having a high aspect ratio was studied [3]. It was observed that the growth direction of nanoholes depends on the crystal orientation of Ga metal. The growth direction of the nanohole was almost coincident with the certain crystal axis of Ga metal when the anodizing voltage was low. The present fabrication process is expected to be applied to fabricate various energy conversion devices requiring a geometrically controlled porous Ga oxide, such as hydrogen generation devices.[1] T. Kondo, Y. Kuroda, T. Shichijo, T. Yanagishita, H. Masuda, J. Vac. Sci. Technol. B, 40, 010603 (2022).[2] H. Masuda, T. Yanagishita, T. Kondo: “Fabrication of Anodic Porous Alumina”, Encyclopedia of Interfacial Chemistry 1st Edition, Elsevier (2018).[3] T. Kondo, Sci. Rep., 13, 12408 (2023).

Reversible Single-Crystal to Single-Crystal Transformation and Associated Magnetism of a Cyanide-Bridged Chiral-Structured Magnet.

A chiral molecule-based magnet [MnII (S-pnH) (H2O)][MnIII(CN)6]·H2O (S-pn = S-1,2-diaminopropane), 1S·2H2O (P212121), has been obtained, which has a two-dimensional (2D) square network of cyanide-bridged MnII-MnIII ions. The crystallographic research on this coordination polymer indicates that it is robust enough to transform the single-crystal structure upon dehydration as well as rehydration. Meanwhile, the magnetic property changes are reversibly associated with the structural phase transitions. The complete reversibility upon dehydration/rehydration was demonstrated using in situ X-ray diffraction from the as-prepared 1S·2H2O to the dehydrated [MnII (S-pnH)][MnIII(CN)6], 1S, then rehydrated to [MnII (S-pnH) (H2O)][MnIII(CN)6]·H2O, 1S-HP, and dehydrated again to [MnII (S-pnH)][MnIII(CN)6], 1S-DeHP. Neither the space groups nor the crystal axes changed during the dehydration/rehydration process. The dehydration is considered to be associated with a change in the coordination of the S-pnH from one 2D layer to the neighboring one involving a proton transfer and is accompanied by new cyanide bridging of MnII and MnIII ions formed between the 2D sheet. Corresponding to the 2D to three-dimensional (3D) structural transition, the study of magnetic properties reveals that the Curie temperature of long-range magnetic ordering for 1S (TC = 45 K) is more than double that for 1S·2H2O (TC = 21 K).

180 mW, 1 MHz, 15 fs carrier-envelope phase-stable pulse generation via polarization-optimized down-conversion from gas-filled hollow-core fiber

Gas-filled hollow core fibers allow the generation of single-cycle pulses at megahertz repetition rates. When coupled with difference frequency generation, they can be an ideal driver for generating carrier-envelope phase stable, octave-spanning pulses in the short-wavelength infrared. In this work, we investigate the dependence of the polarization state in gas-filled hollow-core fibers (HCF) on the subsequent difference frequency generation stage. We show that by adjusting the input polarization state of light in geometrically symmetric systems, such as hollow-core fibers, one can achieve precise control over the polarization state of the output pulses. This manipulation preserves the temporal characteristics of the generated ultrashort pulses, especially when operating at a near single-cycle regime. We leverage this property to boost the downconversion efficiency of the near single-cycle pulses in a type I difference frequency generation stage. Our technique overcomes the bandwidth and dispersion constraints of the previous methods that rely on broadband waveplates or adjustment of crystal axes relative to the laboratory frame. This advancement is crucial for experiments demanding pure polarization states in the eigenmodes of the laboratory frame.

Thin film lithium niobate electro-optic modulator with reduced half-wave voltage length product through design

This paper aims at shortening electrode spacing in a thin film lithium niobate (TFLN) electro-optic modulator (EOM) while avoiding an increase in metal absorption loss, thereby reducing the half-wave voltage length product (V π ⋅L). Through numerical simulations, we find that metal absorption loss reaches its peak values when the optical modes of the metal-clad dielectric waveguide and ridged waveguide hybridize. This negative effect can be mitigated by adjusting the electrode width to modify the optical mode of the metal-clad dielectric waveguide. In addition, we raise the vertical position of the electrodes to further mitigate metal absorption loss and reduce the electrode spacing. By calculating the optimal buffer layer thickness for two crystal axis orientations, our findings reveal a 19% reduction in V π ⋅L at conventional crystal axis orientation (θ=±90∘) and a 16% decrease at unconventional crystal axis orientation (θ=54∘). Notably, V π ⋅L at unconventional crystal axis orientation is 5% lower than at conventional crystal axis orientation. These findings demonstrate the effectiveness of geometric configuration optimization toward enhancing the efficiency and performance of the TFLN EOM.

Accumulation of oxygen interstitial-vacancy pairs under irradiation of corundum single crystals with energetic xenon ions

Single crystals of α-Al2O3 with broad sides oriented perpendicular to the c crystal axis have been irradiated by 231-MeV xenon ions with fluence varying from 5 × 1011 to 1014 ions/cm2. The spectra of radiation-induced optical absorption (absorption of a pristine crystal is subtracted) have been decomposed into Gaussians serving as a measure of oxygen-related Frenkel defects (interstitial-vacancy pairs). The concentration of all structural defects considered – vacancy-type F and F+ centers as well as oxygen interstitials – continuously increases with ion fluence. Therefore, radiation-induced origin of elementary absorption bands at 5.6 and 6.6 eV tentatively ascribed earlier to charged and neutral oxygen interstitials has been proved for the first time. The concentrations of charged interstitials (in the form of superoxide ions) have been directly determined by the EPR method. The evolution of cathodoluminescence bands typical of self-trapped excitons (VUV band at 7.6 eV) and F-type defects (bands peaked around 3.0 and 3.8 eV) with the rise of Xe-ion-irradiation fluence has been measured and analyzed.

ON THE POSSIBILITY OF USING STRAIGHT AND BENT CRYSTALS FOR CHARGED PARTICLE BEAM STEERING AT THE FUTURE MULTIFUNCTIONAL ACCELERATOR COMPLEX OF NSC KIPT

The scattering of electrons and positrons with energy of 500 MeV on straight and bent silicon crystals has been considered using numerical simulations. The selected particle energy corresponds to parameters that can be achieved at the future multifunctional accelerator complex of the NSC “Kharkiv Institute of Physics and Technology”. It is shown that bent crystals, at certain orientations, allow deflecting charged particles at angles significantly exceeding the critical angle of axial channeling. It is also shown that experimental investigation of the effect of reducing inco- herent scattering of high-energy positrons when orienting the crystal relative to the direction of particle incidence near one of the main crystal axes is of interest.

The role of losses in determining hyperbolic material figures of merit

Uniaxial materials have achieved new prominence in photonics because they can have hyperbolic spectral regions with metallic (ε<0) and dielectric (ε>0) permittivities along different crystal axes. In the lossless case, this results in an open hyperboloid dispersion relation, allowing materials to support highly confined modes with extremely large wavevectors. However, even small losses change the character of the hyperbolic dispersion from open hyperboloids to closed surfaces with finite maximum k, significantly limiting the extent to which highly-confined modes can be achieved. Here, we derive a simple analytic formula for the dispersion relation in the presence of loss and show that for some typical materials the maximum wavevector in hyperbolic materials is roughly ten times the free-space. The scaling of the maximum wavevector is derived, and it is shown that there is a universal scaling relation between the propagation length and the wavelength, which implies that the shortest wavelengths in any hyperbolic material are strongly attenuated.

Tracing of low-energy protons implanted in different Si crystal orientations by keV recoil detection in transmission geometry

The potential of recoil detection in transmission geometry in examining a possible preferential lattice site location of H atoms implanted into thin single crystalline silicon membranes is explored. Low-energy protons were directed onto the membranes along the 〈001〉 Si crystal axis, as well as in random orientation. Position-sensitive and time-resolved detection of recoiling hydrogen species from a pulsed beam of 280 keV 22Ne+ primary ions was performed in a time-of-flight medium energy ion scattering system. From the primary beam incidence along different crystal axes, a preferential detection of recoiled hydrogen along the 〈011〉 axis can be revealed, as compared to the 〈001〉 axis. The present approach and possible future developments potentially enabling real-space location of interstitial hydrogen are discussed.

Structural Phase Transitions of Mg2NiH4 Induced by NiH4 Molecular Ion Distortion and Metal Lattice Deformation under High Pressures.

Experimental observations indicate that pressure treatments transform the monoclinic and orthorhombic low-temperature phases of Mg2NiH4 into an unresolved pseudocubic phase even at room temperatures, resembling the temperature-induced phase transformation of the material. This pressure-induced phase transformation is anticipated to involve deformations of the tetrahedrally bonded NiH4 molecular ion and the metal lattice. However, the precise mechanism underlying this transformation remains unclear. To elucidate this behavior, this study adopted first-principles density functional theory calculations to investigate the effect of applied pressure on the observed phase transition. The results revealed that the phase transition from the low-temperature phases to the pseudocubic phase occurs at approximately 8-9 GPa. Furthermore, at this pressure, the metal lattice deforms into an antifluorite-like structure, and the NiH4 molecular ion undergoes substantial distortion, resulting in the alignment of hydrogen atoms along the crystal axes of the metal lattice. Furthermore, through a comprehensive structural exploration, we successfully identified several tetragonal and orthorhombic models that are energetically more stable than the low-temperature phases at low pressures. These models are potential candidates for elucidating the pseudocubic phase observed in experiments. Overall, our findings are anticipated to enhance the current understanding of the structural changes occurring during pressure and temperature-induced phase transitions.

Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment

Abstract We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 µm is found to be ∼ 10 − 2 . We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor &gt; 10 3 using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of ϵ x ∼ 10 − 5 on spectator qubits, demonstrating a suppression of crosstalk error by a factor of &gt; 10 2 . We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.